1. Field of the Invention
The present invention relates to a medical image processing device for producing an image in which a difference in color between a normal site and a lesion site is enhanced, a method for operating a medical image processing device, and an endoscope system.
2. Description Related to the Prior Art
In medical fields, diagnoses utilizing endoscope systems have been widely performed. The endoscope system comprises a light source device, an endoscope, and a processor device. In the endoscope system, illumination light is applied from an endoscope to a region of interest (Object), and the object under the illumination light is imaged with an imaging element of the endoscope. An image of the object is displayed on a monitor based on an image signal obtained by imaging the object. A doctor detects the presence or absence of a lesion while observing the image displayed on the monitor.
It is easy to detect a lesion (e.g. protrusion from mucosal surface) which significantly differs from a normal site (normal portion) in shape and size. However, in the case where a lesion is similar to the normal portion in shape and size, the lesion is detected based on a difference in color from that of the normal portion. It is extremely difficult to detect the lesion in a case where the lesion is in its early stage and there is little difference in color between the lesion and the normal portion.
In Japanese Patent No. 3228627, a difference in color between the normal portion and the lesion is made clearly visible by a process to further move the value of a portion, which is displaced from a reference value of blood volume (hemoglobin index), away from the reference value.
It is known that gastric (stomach) cancer causes atrophy of gastric mucosa (mucous membrane layer of the stomach), which makes the color of the gastric mucosa to fade. For this reason, there is a difference in color between the atrophic mucosa and the normal mucosa. The stomach cancer is diagnosed by observing the difference in color between the suspected lesion and the normal portion with an endoscope. “ABC method (ABC screening)” is recommended by the authorized nonprofit organization “Japan Research Foundation of Prediction, Diagnosis and Therapy for Gastric Cancer”.
In advanced stages of atrophy (for example, groups C or D in the ABC screening), the difference in color between the normal portion and the atrophic portion is clear, so that it is easy to detect the atrophic portion. However, in intermediate stages (for example, groups B and C in the ABC screening), there is little difference in color between the atrophic portion and the normal portion. Therefore it is difficult to detect the atrophic portion based only on the difference in color. It is necessary to enhance the difference in color between the atrophic portion and the normal portion to facilitate the detection of the atrophic portion even if there is little difference in color between them.
Note that the difference in color between the atrophic portion and the normal portion may be enhanced using a method described in Japanese Patent No. 3228627. However, the color of the atrophic portion is affected not only by the blood volume but also by factors other than the blood volume. Therefore it is difficult to enhance the difference in color between the atrophic portion and the normal portion with the use of the method described in the Japanese Patent No. 3228627.